Method of internally masking hollow articles



1958 K. JAMES EIAL 2,855,326

METHOD OF INTERNALLY MASKING HOLLOW ARTICLES Filed April 27, 1956 IN V EN TORJ KENNETH JAMES United States Patent METHOD OF INTERNALLY MASKING HOLLOW ARTICLES Kenneth James, Melrose, and Ernest F. Stacey, Hamilton, Mass., assignors to Sylvania Electric Products Inc., Salem, Mass., a corporationof Massachusetts Application April 27, 1956, Serial No. 581,070

6 Claims. (Cl. 117-38) This invention relates generally to processes for depositing reflective coatings on the inner surfaces of lamp bulbs and more particularly to methods of masking areas of said bulbs which are to remain clear.

In the manufacture of reflector lamps a portion of the bulb is internally coated with reflective material before the bulb is sealed to a mount or sub-assembly of internal elements. The coating operation is generally effected by vaporizing a quantity of metal-such as aluminum, silver or gold within the bulb after the latter has been evacuated. The vaporized metal is thereby deposited upon exposed interior surfaces of the bulb. Surfaces which are intended to be kept clear to permit passages of light therethrough are suitably masked during the coating operation.

It has been found convenient to employ a measured quantity of granular material, such as small glass beads, to cover the portion of such bulbs which is to be left clear. In the conventional method of masking with such material, the bulb which includes an open neck and a closed bowl portion is supported in a vertical neck-up position. The granular material is then poured into the bowl portion through the neck. Thereafter the bulb is rotated, oscillated or otherwise agitated to distribute the masking material in order to provide an even mask line which defines the end of the coated portion.

The conventional method has a number of serious disadvantages. In the first place, the movement of the bulb to distribute the masking material is time consuming and the coating process is accordingly slowed down. Another disadvantage is that variations in the distributing motions result in irregularity of the mask line. Still another disadvantage is that, the absence of control over the coating material while it is being poured into the bulb and thereafter agitated by movement of the latter allows grains or beads to be deposited on the portion of the bulb which is to be coated. These beads leave objectionable pinholes in the coating when they are removed after the completion of the coating operation.

It is accordingly an object of our invention to provide a method for distributing granular masking material within lamp bulbs to provide an even mask line.

Another object is to provide a method of obtaining an even mask line without the need of moving the masking material after it is initially delivered to the bulb.

A further object is to provide a method of introducing masking material into a bulb with such control over the material that adhesion of particles to the wall of the bulb is substantially eliminated.

The foregoing and other objects are achieved in accordance with our invention by employing a tube which restricts and directs motion of the masking material as it is delivered to the bulb. The tube is positioned vertically in the bulb which is supported in neck-up position. The lower end of the tube is maintained close to the inside of the bowl portion of the bulb which effectively closes the tube to passage of material therethrough. The masking material is then poured into the tube which is thereafter raised thereby effecting an even flow of material in all directions. The resulting body of masking material in the bulb has an upper surface which provides an even mask line without further displacement of the masking material.

Further objects and advantages of our invention will appear from the following detailed description of one of its species taken in connection with the accompanying drawing in which:

Figure l'is a view in elevation and partly in section of a lamp including a bulb having a reflective coating with the application of which our invention is related;

Figure 2 is a view in elevation of a bulb showing a tube positioned therein to receive masking material;

Figure 3 is a view in elevation of the bulb after the masking material has been poured into the tube; and

Figure 4 is a view in elevation of the bulb showing the disposition of the masking material therein as the tube is removed. I

Turning to the drawings, a lamp including a bulb or envelope, indicated at 10 and having an internal reflective coating 12 is shown in Fig. 1. It will be convenient at the outset to think of the envelope as including a face 14 and a rear portion 16. The face 14 is kept clear by being masked during the coating operation whereas the reflective coating 12 which terminates at a mask line 18 is applied to the portion 16. A neck 20 is part of the portion 16 and supports a base 22. Lead-in wires 24 sealed in the bulb 10 support a filament 25 between their inner ends and are connected at their outer ends to appropriate terminals on the base 22.

With reference to Figures 2-4 we will now describe our method of depositing granular masking material such as a body of glass beads 26 into the bulb 10 to produce an even mask line 18. As shown in these views, the bulb 10 is supported in neck-up position in a suitable cradle or nest 28. The bulb 10 is preferably provided with additional lateral support such as a V-shaped member 30. A tube 32 is positioned into the vertically supported bulb 10 with the lower end of the tube in close proximity to the face 14 or in actual contact with it. In order to facilitate the pouring of beads 26 into the tube 32 the upper end portion of the latter may conveniently be funnelshaped as shown.

With the tube 32 held central and vertical in the bulb 10, a measured quantity of beads 26 is poured into the tube, the lower end of which is effectively closed by the face 14 as shown in Figure 3.

Thereafter, the tube 32 is withdrawn upwardly to free the beads 26 which travel evenly in all directions under the vertical pressure of the beads above them in the tube. Best results are obtained in distributing the beads 26 evenly if the tube 32 is raised without introducing a sizable horizontal motion component.

After the face 14 has been masked by our method, the reflective coating 12 may be applied to the portion 16 of the bulb 10 by a conventional process not otherwise related to our invention. In applying the coating, a small quantity of aluminum, for instance, is placed on an electrically energized vaporizer element inside the bulb 10. The neck 20 is suitably sealed; the bulb is then evacuated; and the vaporizer element is energized to flash the coating metal onto exposed internal surfaces of the bulb 10.

What we claim is:

l. The method of internally masking a selected portion of a lamp bulb having a closed bowl portion and a single open neck, said method comprising: supporting said bulb in vertical neck-up position; positioning a straight tube partially within said vertically supported bulb, said tube in said position having its lower end in proximity with the inner surface of said bowl and its upper end extending above said neck; pouring a predetermined quantity of granular masking material into said tube; and thereafter effecting relative motion between said bulb and said tube to increase the distance between the lower end of the latter and the inner surface of the bowl whereby an even mask line is produced.

2. The method of internally masking a selective portion of a lamp bulb having a closed bowl portion anda single open neck, said method comprising: supporting said bulb in vertical neck-up position; positioning a straight tube partially within said vertically supported bulb, said tube in said position having its lower end in proximity with the inner surface of said bowl and its upper end extending above said neck; pouring a predetermined quantity of granular masking material into said tube; and thereafter raising said tube to distribute said material uniformly in all directions whereby an even mask line is produced.

3. The method of internally masking a selected portion of a lamp bulb having a closed bowl portion and a single open neck, said method comprising: supporting said bulb in vertical neckup position; positioning a straight tube partially within said vertically supported bulb, said tube in said position having its lower end resting on the inner surface of the bowl and closed thereby and its upper end extending above said neck; pouring a predetermined quantity of granual masking material into said tube; and thereafter raising said tube from said bowl to distribute said material uniformly in all directions whereby an even mask line is produced.

4. The method of internally masking a selected portion of a lamp bulb having a closed bowl portion and a single open neck, said method comprising the following steps: supporting said bulb in vertical neck-up position; positioning a straight tube partially within said vertically supported bulb, said tube in said position being coaxial with the bulb having its lower end in proximity with the inner surface of said bowl and its upper end extending above said neck; pouring a predetermined quantity of fine glass beads into said tube; and thereafter raising said tube to distribute said beads uniformly in all directions thereby providing a body of beads for masking a portion of the inner surface of said bowl, said body having an upper surface which defines an even mask line at its outer edges.

5. The method of internally masking a selected portion of a lamp bulb having a closed bowl portion and a single open neck, said method comprising the following steps: supporting said bulb in vertical neck-up position; positioning a straight tube partially within said vertically supported bulb, said tube in said position being coaxial with the bulb, having its lower end resting on the inner surface of the bowl and closed thereby and its upper end extending above said neck; pouring a predetermined quantity of glass beads into said tube; and thereafter raising said tube to distribute said beads uniformly in all directions thereby providing a body of beads for masking a portion of the inner surface of said bowl, said body having an upper surface which defines an even mask line at its outer edges.

6. The method of internally masking a selected portion of a lamp bulb having a closed bowl portion and a single open neck, said method comprising the following steps: supporting said bulb in vertical neck-up position; positioning a straight tube partially within said vertically supported bulb so that said tube is coaxial with said bulb, its lower end is in proximity to the inner wall of said bowl and its upper end extends above said neck; pouring a predetermined quantity of granual material into said tube; and thereafter guiding said tube upwardly to distribute said beads uniformly in all directions thereby providing a body of beads for masking a portion of the inner surface of said bowl, said body having an upper surface which defines an even mask line at its outer edges.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF INTERNALLY MASKING A SELECTED PORTION OF A LAMP BULB HAVING A CLOSED BOWL PORTION AND A SINGLE OPEN NECK, SAID METHOD COMPRISING: SUPPORTING SAID BULB IN VERTICAL NECK-UP POSITION; POSITIONING A STRAIGHT TUBE PARTIALLY WITHIN SAID VERTICALLY SUPPORTED BULB, SAID TUBE IN SAID POSITION HAVING ITS LOWER END IN PROXIMITY WITH THE INNER SURFACE OF SAID BOWL AND ITS UPPER END EXTENDING ABOVE SAID NECK; POURING A PREDETERMINED QUANTITY OF GRANNULAR MASKING MATERIAL INTO SAID TUBE; AND THEREAFTER EFFECTING RELATIVE MOTION BETWEEN SAID BULB AND SAID TUBE TO INCREASE THE DISTANCE BETWEEN THE LOWER END OF THE LATTER AND THE INNER SURFACE OF THE BOWL WHEREBY AN EVEN MASK LINE IS PRODUCED. 